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28 results on '"Lis T"'

27. The cis-trans isomerization of N-methyl-α,β-dehydroamino acids.

Author

Siodłak D, Macedowska-Capiga A, Broda MA, Kozioł AE, and Lis T

Subjects
Acetonitriles chemistry, Chloroform chemistry, Crystallography, X-Ray, Magnetic Resonance Spectroscopy, Models, Molecular, Peptides chemical synthesis, Spectroscopy, Fourier Transform Infrared, Stereoisomerism, Acids chemistry, Amides chemistry, Molecular Conformation, Peptides chemistry
Abstract

Dehydroamino acids with the methylated N-terminal peptide group occur in natural small cyclic peptides. The structural analysis was used to investigate the cis-trans isomerization of the N-terminal tertiary amide group of diamides: Ac-(Z)-Δ(Me)Abu-NHMe (1), Ac-(Z)-Δ(Me)Phe-NHMe (2), Ac-(E)-Δ(Me)Phe-NHMe (3), Ac-Δ(Me)Ala-NHMe (4), and Ac-(Me)Ala-NHMe (5). The compounds were analyzed in the solid state by an X-ray crystallography (1-3), and in the solution by FTIR (MeCN and CHCl(3) ) and NMR (DMSO-d6 and CDCl(3) ) methods (1-5). In the solid state, the studied compounds adopt the cis configuration of N-terminal amide. In solution, this configuration also prevails for the dehydroamino acids 1-4, in contrast to the saturated analog 5. The results indicate that N-methyldehydroamino acids present a promising tool to induce the cis configuration of the amide bond., (Copyright © 2012 Wiley Periodicals, Inc.)

Published
2012
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28. Combined effect of the DeltaPhe or DeltaAla residue and the p-nitroanilide group on a didehydropeptides conformation.

Author

Lisowski M, Latajka R, Picur B, Lis T, Bryndal I, Rospenk M, Makowski M, and Kafarski P

Subjects
Alanine chemistry, Circular Dichroism, Crystallography, Magnetic Resonance Spectroscopy, Models, Molecular, Phenylalanine chemistry, Protein Conformation, Spectroscopy, Fourier Transform Infrared, Alanine analogs & derivatives, Amides chemistry, Dipeptides chemistry, Models, Chemical, Phenylalanine analogs & derivatives
Abstract

Two series of dehydropeptides of the general formulae Boc-Gly-X-Phe-p-NA, Boc-Gly-Gly-X-Phe-p-NA, Gly-X-Gly-Phe-p-NA.TFA, and Boc-Gly-X-Gly-Phe-p-NA, with X = Delta(Z)Phe and DeltaAla, were studied with NMR in DMSO and CDCl(3)-DMSO, and with CD in MeOH, MeCN, and TFE. The NMR spectra measured in DMSO suggest that peptides with the DeltaPhe residue next to Phe are folded whereas peptides with Gly between DeltaPhe and Phe are less ordered. NMR spectra of DeltaAla-containing peptides indicate that these peptides are flexible and their conformational equilibria are populated by many different conformations. The CD spectra show that conformational properties of the peptides studied are distinctly influenced by a mutual position of the dehydroamino acid residue and the p-NA group. They indicate that all dehydropeptides with the DeltaPhe residue, Boc-Gly-DeltaAla-Phe-p-NA, and Boc-Gly-Gly-DeltaAla-Phe-p-NA adopt ordered conformations in all solvents studied, presumably of the beta-turn type. The last two peptides exhibit surprising chiroptical properties. Their spectra show exciton coupling-like couplets in the region of the p-NA group absorption. This shape of CD spectra suggests a rigid, chiral conformation with a fixed disposition of the p-NA group. The CD spectra indicate that Boc-Gly-DeltaAla-Gly-Phe-p-NA and Gly-DeltaAla-Gly-Phe-p-NA.TFA are unordered, independently of the solvent., (2007 Wiley Periodicals, Inc)

Published
2008
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